President Trump confirmed Friday that he will nominate former attorney general William P. Barr to lead the Justice Department again — bringing relief to department veterans who had feared a more unconventional pick but generating some concern among lawmakers about the future of the special counsel investigation into Russian interference in the 2016 election.

Trump told reporters Friday that Barr had been “my first choice since day one” and praised the man he hopes will be his attorney general as having “demonstrated an unwavering adherence to the rule of law.”

“There is no one more capable or qualified for this role,” the president said at a Justice Department event in Kansas City, Mo. He predicted that his nominee would “probably get” bipartisan support.

Barr, 68, is indeed a well-respected lawyer who is well known in conservative circles. He served as attorney general from 1991 to 1993 under President George H.W. Bush and before that as deputy attorney general, the No. 2 official.

After leaving the department, he spent many years in the corporate world — as general counsel and executive vice president of GTE Corp., and later, after a merger, in the same position at Verizon Communications. He most recently worked in private practice at Kirkland & Ellis, advising corporations on government enforcement matters.

Barr’s corporate work is likely to draw significant scrutiny as he heads toward a confirmation hearing. Democrats and even some Republicans said they would like assurances that he would let special counsel Robert S. Mueller III’s investigation proceed normally before voting to confirm him.

Barr has in the past questioned the political makeup of Mueller’s team — which has many Democratic donors, though Mueller himself is a Republican — and expressed sympathy toward Trump’s firing of FBI Director James B. Comey.

Sen. Susan Collins (R-Maine) said she wants assurances that Barr would allow Mueller’s probe to continue.

“That would be one of the issues that I certainly would want to make sure, and that he recognizes that not only that Mr. Mueller has to be allowed to complete his investigation unimpeded, but also that prosecutorial decisions that are made by the department need to be independent,” she said.

Democrats were more forceful. Sen. Dianne Feinstein (Calif.), the ranking Democrat on the Senate Judiciary Committee, said in a statement that Barr “must commit to supporting Special Counsel Mueller’s investigation and allowing him to follow the facts.”

Sen. Charles E. Schumer (D-N.Y.) said in a statement that Barr would “have a steep hill to climb in order to be confirmed by the Senate.”

“Mr. Barr must commit — at a minimum — under oath before the Senate to two important things: First, that the Special Counsel’s investigation will proceed unimpeded, and second, that the Special Counsel’s final report will be made available to Congress and the public immediately upon completion,” Schumer said.

In a brief phone conversation Friday, Barr confirmed that he had accepted the president’s offer but declined to comment further. A spokesman for the Senate Judiciary Committee said his confirmation hearing would not occur before the end of the year, given the limited time left before a new Senate takes over on Jan. 3.

People familiar with the process said that while Trump had long said he preferred an attorney general he knew, Barr was highly recommended by people in the president’s orbit — including acting White House counsel Emmet Flood and Federalist Society Executive Vice President Leonard Leo.

Barr did not seek the job, people familiar with the matter said, at first recommending others he thought might be suitable, including former federal judge J. Michael Luttig. Several others were considered — including former New Jersey governor Chris Christie (R), Florida Attorney General Pam Bondi (R) and Rep. John Ratcliffe (R-Tex.).

But Trump himself quickly settled on Barr, and the former attorney general was convinced he should return to government out of a sense of duty, people familiar with the matter said.

“His friends were telling him he’s not getting these calls for the good of his ego, he’s getting calls because ‘they need you,’ ” one person said.

Within the Justice Department, the selection of Barr was received with a degree of relief, as he is viewed as someone who has long-standing ties to the building and knows how its various offices operate, according to several current and former officials.

Former New Hampshire governor John H. Sununu, who was George H.W. Bush’s chief of staff when Barr was attorney general, said Barr was “always very precise, very clear in what could and couldn’t be done, and what should and shouldn’t be done.” He said that when he learned Barr had been chosen again, he was “happy for America.”

Even though it has been decades since Barr ran the Justice Department, he has stayed in touch with its leaders and staff. This summer, Deputy Attorney General Rod J. Rosenstein invited Barr to speak to the political appointees, and the former attorney general urged them to ignore the political noise and focus on their work, according to a person familiar with the private event.

In recent days, Rosenstein had spoken to the president about the selection process and was “ecstatic” with the choice of Barr, this person said. Barr was also close with Jeff Sessions and the two spoke frequently when Sessions was attorney general, this person said.

Trump’s relationship with his previous attorney general was severed in large part because Sessions had recused himself from the Russia matter before Mueller’s appointment by Rosenstein. Trump launched a new round of attacks on Mueller on Friday, tweeting about what he called Mueller’s “big time conflicts of interest” and saying he planned to do “a major Counter Report to the Mueller Report.”

“This should never again be allowed to happen to a future President of the United States!” Trump wrote.

Barr shares at least one of the president’s views on Mueller’s team. In 2017, when asked by The Washington Post about political donations made by lawyers on the special counsel’s team, Barr said that “prosecutors who make political contributions are identifying fairly strongly with a political party,” and added: “I would have liked to see [Mueller] have more balance on this group.”

That piece was written before many of the details of Comey’s private interactions with Trump became known.

“I like and respect Bill Barr. I know he’s an institutionalist who cares deeply about the integrity of the Justice Department, so I’m sure he’ll use standard career resources he has to judge what he should be involved in and shouldn’t be involved in,” said Comey, speaking on Capitol Hill. “But Bill Barr is a talented person who was a good attorney general the first time. I liked him very much then. I think he’ll serve the Justice Department well.”

Barr also wrote in an op-ed months earlier that the president was right to fire acting attorney general Sally Yates after she refused to defend a controversial travel-ban executive order issued in the first days of the administration.

Other skeptics have pointed to Barr’s assertion a year ago to the New York Times that he saw more basis to investigate Hillary Clinton over an old corporate acquisition involving a uranium company than possible collusion between Trump and Russia, though he spoke in conditional language. “To the extent it is not pursuing these matters, the department is abdicating its responsibility,” Barr said.

Sen. Lindsey O. Graham (R-S.C.), who will take over as chairman of the Senate Judiciary Committee next year, said in a statement that Barr is “highly capable, highly respected and will provide new and much-needed leadership for the Department of Justice.”

“I will do everything in my power to push him through the Senate Judiciary Committee and onto the floor of the Senate for eventual confirmation as soon as possible,” Graham said.

In an interview Friday, former attorney general John D. Ashcroft said it would be difficult to name someone who “would deserve a higher level of bipartisan support” in the Senate than Barr.

Asked whether he thinks Barr would be able to withstand any pressure from Trump when it comes to the special counsel investigation, Ashcroft said: “I have every confidence that Bill Barr will do the right thing in any circumstance or situation.”

Until Barr takes over, the department will continue to be led by acting attorney general Matthew G. Whitaker, who has drawn fierce criticism for his past business dealings and his public criticism of Mueller’s investigation.

Whitaker, who traveled with Trump on Air Force One to Kansas City, called Barr a “continuation of this law-and-order president.”

“Bill is supremely qualified, highly respected at the Department of Justice and will continue to support the men and women in blue,” Whitaker said in Kansas City as he introduced Trump. “I commend the president for this excellent choice.”